in the paper-input, tabindex attribute is applied to the container not the input

when creating a paper-input element like
```
{{paper-input
value=email
label='email'
class="flex-100 md-block"
tabindex='1'
type="email"
autofocus="true"
onChange=(action (mut email))
required=true
}}
```
the created html looks like
```html

email

````

so the problem here is the tabindex value is applied to the md-input-container element rather than passed through to the input element. That has the effect of tabbing landing on the label and the next tab landing on the input (two tabs), rather than directly on the input (one tab).